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? 以前做一個看書的項目時,有個翻書的功能,當手指滑動書頁移動一段然后抬起后,需要頁面view自動完成剩余的操作:
1、當滑動距離大于某個設定值時,自動滾動到末尾處,翻一頁。
2、當滑動距離小于該設定值時,自動回滾到起始處,還原。
? 實現這個功能,當時是用了Scroller來實現的,由于自己還是菜鳥,搞了老久沒懂,最近看android時,猛然發現,原來是這樣啊。
? 我一步步來說下吧:
1、Scroller的最簡單用法解釋
? 網上有很多關于Scroller的用法,很多講的真的很不錯,但我覺得,他們的講解還是過于繁瑣,這里我就最最簡單的說下吧,這個Scroller到底怎么回事,且看下面代碼:
scrollview、 ? ?下面的這個demo1,就一個布局,linearlayout上放置一個button,點擊button,我們就調用Scroller的相關方法:
布局文件xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><Buttonandroid:id="@+id/button1"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_alignLeft="@+id/textView1"android:layout_margin="10dp"android:text="run Scroller " />
</LinearLayout>
控制器activity:
package cn.helloclq.nb.scroller;import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.LinearLayout;
import android.widget.Scroller;public class MainActivity extends Activity {private Scroller mScroller;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);mScroller = new Scroller(this);this.setContentView(R.layout.activity_main); findViewById(R.id.button1).setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {mScroller.startScroll(-10, -100,- 200, -300, 1000);new Thread(){public void run() {while(mScroller.computeScrollOffset())// 如果mScroller沒有調用startScroll,這里將會返回false。{Log.i("scroller", "getCurrX()= "+mScroller.getCurrX()+" getCurrY()="+mScroller.getCurrY());try {Thread.sleep(50);} catch (InterruptedException e) {e.printStackTrace();}}};}.start();}});}
}
運行后,點擊按鈕,就可以看到效果,且看控制臺日志輸出: android cursor、
05-02 11:30:55.455: I/scroller(30287): getCurrX()= -10 getCurrY()=-100
05-02 11:30:55.510: I/scroller(30287): getCurrX()= -26 getCurrY()=-124
05-02 11:30:55.557: I/scroller(30287): getCurrX()= -63 getCurrY()=-180
05-02 11:30:55.612: I/scroller(30287): getCurrX()= -111 getCurrY()=-251
05-02 11:30:55.658: I/scroller(30287): getCurrX()= -144 getCurrY()=-301
05-02 11:30:55.713: I/scroller(30287): getCurrX()= -166 getCurrY()=-334
05-02 11:30:55.760: I/scroller(30287): getCurrX()= -181 getCurrY()=-356
05-02 11:30:55.815: I/scroller(30287): getCurrX()= -191 getCurrY()=-371
05-02 11:30:55.862: I/scroller(30287): getCurrX()= -197 getCurrY()=-381
05-02 11:30:55.916: I/scroller(30287): getCurrX()= -201 getCurrY()=-387
05-02 11:30:55.963: I/scroller(30287): getCurrX()= -204 getCurrY()=-391
05-02 11:30:56.018: I/scroller(30287): getCurrX()= -206 getCurrY()=-394
05-02 11:30:56.065: I/scroller(30287): getCurrX()= -208 getCurrY()=-396
05-02 11:30:56.119: I/scroller(30287): getCurrX()= -208 getCurrY()=-398
05-02 11:30:56.166: I/scroller(30287): getCurrX()= -209 getCurrY()=-398
05-02 11:30:56.221: I/scroller(30287): getCurrX()= -209 getCurrY()=-399
05-02 11:30:56.268: I/scroller(30287): getCurrX()= -210 getCurrY()=-399
05-02 11:30:56.322: I/scroller(30287): getCurrX()= -210 getCurrY()=-400
05-02 11:30:56.369: I/scroller(30287): getCurrX()= -210 getCurrY()=-400
05-02 11:30:56.424: I/scroller(30287): getCurrX()= -210 getCurrY()=-400
05-02 11:30:56.471: I/scroller(30287): getCurrX()= -210 getCurrY()=-400
從日志輸出的數據一看,你應該能大致知道這個scroller的作用了吧
mScroller.startScroll(-10, -100,- 200, -300, 1000);
我們在button的事件處理里做的是調用了 public void?startScroll?(int startX, int startY, int dx, int dy,int?duration)? 這個方法,然后我們在線程中一直查看scroller的幾個屬性數值,然后打印了出來,從日志可以看出,scroller中的這些數值,是按(int startX, int startY, int dx, int dy)來變化的,并且是在intduration這個時間段內完成的。我們設置線程的睡眠時間是50毫秒,而打印了總共20條日志,20* 50 = 1000,正好是我們設置的這個時間。
? 如果我們在調用了public void?startScroll?(int startX, int startY, int dx, int dy,in tduration) ?,讓我們的view重新繪制,并且利用scroller的幾個屬性數值來確定view的位置或其他的什么,然后不斷的循環調用,你說會出現什么呢?答案就不用說了吧(view會動起來吧),這個就是我們平時在項目中利用scroller的主要思路了,而一般的時候,我們會多繞了幾道彎兒而已。
對自我的理解? 2、Scroller結合view的用法
? 首先,我們簡單的介紹下view,查看android的源碼,你會發現如下的方法:
/**
* Called by a parent to request that a child update its values for mScrollX
* and mScrollY if necessary. This will typically be done if the child is
* animating a scroll using a {@link android.widget.Scroller Scroller}
* object.
*/
public void computeScroll()
{
}
該方法就是留給我們去覆寫的,它一般都會被該view的父類viewGroup在繪制該view時調用,具體的,就不多說了,大家可以參見相關博客,如果我們在這個方法里,調用 scroller的相關屬性來修改view的相關屬性或調用其他方法,是不是可以做很多事呢? ? 下面看看改造后的demo2:
先介紹一個函數,view下面的:
Android,
public void scrollTo (int x, int y) Added in API level 1
Set the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int) and the view will be invalidated.Parameters
x the x position to scroll to
y the y position to scroll to
該函數可以使view中的內容滾動到指定位置: demo2:
該demo沒有xml,直接就一個activity:
package cn.helloclq.nb.scroller;import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Scroller;public class MainActivity extends Activity {LinearLayout demoSubview1, demoSubview2, demoViewGroup;private Scroller mScrollerViewGroup;private Scroller mScrollerView;
// private Scroller mScroller;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);mScrollerViewGroup = new Scroller(this);mScrollerView = new Scroller(this);demoSubview1 = new DemoView(this);demoSubview2 = new DemoView(this);demoSubview1.setBackgroundColor(this.getResources().getColor(android.R.color.darker_gray));demoSubview2.setBackgroundColor(this.getResources().getColor(android.R.color.white));demoViewGroup = new DemoViewGroup(this);demoViewGroup.setOrientation(LinearLayout.VERTICAL);LinearLayout.LayoutParams p0 = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT,LinearLayout.LayoutParams.FILL_PARENT);this.setContentView(demoViewGroup, p0);LinearLayout.LayoutParams p1 = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT,LinearLayout.LayoutParams.FILL_PARENT);p1.weight = 1;demoViewGroup.addView(demoSubview1, p1);LinearLayout.LayoutParams p2 = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT,LinearLayout.LayoutParams.FILL_PARENT);p2.weight = 1;demoViewGroup.addView(demoSubview2, p2);DemoButton btn1 = new DemoButton(this);btn1.setText("run Scroller in viewGroup");btn1.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {mScrollerViewGroup.startScroll(-10, -100,- 200, -300, 1000);new Thread(){public void run() {while(mScrollerViewGroup.computeScrollOffset())// 如果mScroller沒有調用startScroll,這里將會返回false。{Log.i("scroller", "getCurrX()= "+mScrollerViewGroup.getCurrX()+" getCurrY()="+mScrollerViewGroup.getCurrY());try {Thread.sleep(50);} catch (InterruptedException e) {e.printStackTrace();}}};}.start();}});demoSubview1.addView(btn1);DemoButton btn2 = new DemoButton(this);btn2.setText("run Scroller in view");btn2.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {mScrollerView.startScroll(-10, -100,- 200, -300, 1000);new Thread(){public void run() {while(mScrollerView.computeScrollOffset())// 如果mScroller沒有調用startScroll,這里將會返回false。{Log.i("scroller", "getCurrX()= "+mScrollerView.getCurrX()+" getCurrY()="+mScrollerView.getCurrY());try {Thread.sleep(50);} catch (InterruptedException e) {e.printStackTrace();}}};}.start();}});demoSubview2.addView(btn2);}class DemoButton extends Button {public DemoButton(Context ctx) {super(ctx);}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);Log.i("DemoButton", "------ onDraw------");}public void computeScroll() {Log.i("DemoButton", " --------------------computeScroll-----------");// Log.i(TAG, "getCurrX = " + mScroller.getCurrX());if (mScrollerView.computeScrollOffset())// 如果mScroller沒有調用startScroll,這里將會返回false。{// 因為調用computeScroll函數的是MyLinearLayout實例,// 所以調用scrollTo移動的將是該實例的孩子,也就是MyButton實例scrollTo(mScrollerView.getCurrX(), 0);Log.i("DemoButton", "getCurrX = " + mScrollerView.getCurrX());// 繼續讓系統重繪invalidate();}}}class DemoView extends LinearLayout {public DemoView(Context ctx) {super(ctx);}@Overridepublic void computeScroll() {Log.i("DemoView", " DemoView --------------------computeScroll-----------");if (mScrollerViewGroup.computeScrollOffset())// 如果mScroller沒有調用startScroll,這里將會返回false。{// 因為調用computeScroll函數的是MyLinearLayout實例,// 所以調用scrollTo移動的將是該實例的孩子,也就是MyButton實例scrollTo(mScrollerViewGroup.getCurrX(), 0);Log.i("DemoView", "getCurrX = " + mScrollerViewGroup.getCurrX());// 繼續讓系統重繪getChildAt(0).invalidate();}}}class DemoViewGroup extends LinearLayout {public DemoViewGroup(Context ctx) {super(ctx);}@Overrideprotected void dispatchDraw(Canvas canvas) {Log.i("DemoViewGroup", "contentview dispatchDraw");super.dispatchDraw(canvas);}}
}
運行程序效果: Android使用自帶文件?
點擊第一個button后,日志如下:
05-02 13:38:02.291: I/DemoViewGroup(332): contentview dispatchDraw
05-02 13:38:02.291: I/DemoView(332): DemoView --------------------computeScroll------
05-02 13:38:02.301: I/DemoButton(332): --------------------computeScroll-----------
05-02 13:38:02.311: I/DemoButton(332): ------ onDraw------
05-02 13:38:02.311: I/DemoView(332): DemoView --------------------computeScroll------
05-02 13:38:02.311: I/DemoButton(332): --------------------computeScroll-----------
05-02 13:38:02.311: I/DemoButton(332): ------ onDraw------
05-02 13:39:50.432: I/scroller(332): getCurrX()= -11 getCurrY()=-101 05-02 13:39:50.432: I/DemoViewGroup(332): contentview dispatchDraw
05-02 13:39:50.432: I/DemoView(332): DemoView --------------------computeScroll------
05-02 13:39:50.432: I/DemoView(332): getCurrX = -12
05-02 13:39:50.442: I/DemoButton(332): --------------------computeScroll-----------
05-02 13:39:50.442: I/DemoButton(332): ------ onDraw------
......................此處省略部分日志...................................................
05-02 13:39:51.412: I/DemoViewGroup(332): contentview dispatchDraw
05-02 13:39:51.412: I/DemoView(332): DemoView --------------------computeScroll------
05-02 13:39:51.412: I/DemoView(332): getCurrX = -210
05-02 13:39:51.412: I/DemoButton(332): --------------------computeScroll-----------
05-02 13:39:51.422: I/DemoButton(332): ------ onDraw------
05-02 13:39:51.432: I/DemoViewGroup(332): contentview dispatchDraw
05-02 13:39:51.432: I/DemoView(332): DemoView --------------------computeScroll------
05-02 13:39:51.432: I/DemoButton(332): --------------------computeScroll-----------
05-02 13:39:51.432: I/DemoButton(332): ------ onDraw------
通過日志,看出什么了沒? 另外,通過該日志,你了解了view的繪畫機制沒,應該能發現吧。
最終的效果圖片:
您正在使用Android,
點擊buttom2,日志就不給出了,效果圖片如下:
button內的文字移動到了不可見處,
所以調用scrollTo移動的將是該view的內容,如果是viewGroup的話,就移動了它的孩子view了
scrollview怎么用?
所以調用scrollTo移動的將是該實例的孩子,也就是MyButton實例
這會兒明白了沒?后面我會嘗試的自己模擬一個scrolelr,其實他的作用就是存儲一些基本的數值,其他的啥也沒做,也和view沒有真正關系的,它只是被動的被調用的